EPIDERMAL APPENDAGES. 317 



temporal and the labial or lip shields. The study of them is 

 simplified by the initial letter of each name being used in 

 reference to them. The names used also speak for them- 

 selves •; as mental, the chin shield ; nasals, near the nostril ; 

 rostral, the beak shields. 



Ophiologists in deciding species, etc., enumerate those 

 which are more than a pair as ' upper labials ' so many, 

 * lower labials ' so many. In some snakes these shields are 

 so large as to cover nearly the entire head ; in others, they 

 are almost inconspicuously small, or absent altogether, and 

 much varied, as we shall see. 



In the vipers the head is generally covered with small, 

 rigid, imbricated, or over-lapping scales instead of plates, and 

 in some the scales are so extremely fine and closely arranged 

 as almost to represent short bristles. This is noticeable in 

 the African 'nose-horned viper' {Vipera nasicornis), -p. 322, 

 where they present a curiously complicated structure. 



Too minute to examine 

 except under the magnify- 

 ing-glass, or to attempt to 



' y Magnified carinated Magnified head-scale of 



only a general idea of these ^^^'^' c'?i'ored'TiSSn°' ^'^ 



curious viper scales, which to the touch are spinous, and 

 rough as a coarse brush. They must form an unpleasant 

 perch for a bird, if it be true that the latter is enticed by the 

 horns of some vipers to come and peck at them, as at a 

 worm. These rigid head-scales become gradually larger and 

 more simple on the body, but are still comparatively small 

 for so large a serpent. In some few of the viperine snakes, 

 plates are present as well as the fine scales, though chiefly 



